A press assembly for electrically testing a printed circuit board

Abstract: A press assembly for performing the electrical test on at least one side of a printed circuit board (200) comprising an upper part (201) and a lower part (202), between which the circuit (200) to be tested is placed, resting on a lower adapter (31), bearing a plurality of needles (30) that can be brought into contact with corresponding spring contacts (24) of a constant gauge grid or needle bed (22), wherein an insulating sheet (20) with a variable thickness is disposed between said adapter (31) and said grid (22) so that adapters (31) of various types can be used, the sheet (20) being provided with holes (23) for the passage of the adapter needle (30).

Description: The present invention relates to a press assembly for electrically testing at least one side of a printed circuit board. As is known, the machines that allow electrical testing of printed circuit boards comprise a press, into which the board to be tested is positioned; e.g. see EP-A-0 050 913. The press comprises at least an adapter which is the element that permits translation between the points of the board being tested and the fixed pitch electrical contact area provided at the level of the press with parallel surfaces. A problem that is encountered with the press assemblies of the known art lies in the fact that a specific adapter must be used for each test machine, since it is not possible to use various types of commercially available adapters on the machine, mainly because of the size differences between them. The aim of the invention is to allow a press assembly for a test machine to be used with adapters of various types, thus constituting an open system for the adapters, without any need for particular modifications. Yet another aim of the invention is to provide a press assembly for a test machine for printed circuit boards that is able to offer the fullest guarantees of reliability and safety in use. The press assembly for performing the electrical test on at least one side of a printed circuit board according to the invention has the characteristics described in the appended claims. Further characteristics and advantages of the invention will be made clearer on examination of the description of a preferred, but not exclusive embodiment of a machine with a press assembly for electrically testing a printed circuit board, illustrated by way of non-limiting example with the aid of the appended drawings, in which: Figure 1 is a schematic perspective view of a test machine seen from the test area side; Figure 2 is a schematic perspective view of the machine seen from the other side, i.e. from the loading area; Figures 3, 4, 5 and 6 schematically illustrate, in sequence, use of the machine directly from the test area, showing the movement of the upper electrical testing head; Figures 7 and 8 are schematic side elevation views of the machine, showing the movements of the upper head of the press assembly; Figure 9 shows schematically the means for moving the upper head; Figure 10 shows the same means as in Figure 9 in a plan block diagram; Figure 11 shows schematically the use of the machine set up for automatic testing, with loading of the circuits on carriers; Figure 12 is a schematic cross section of the carrier handling system, taken for example along the line XII-XII in Figure 11; Figures 13a, 13b and 13c are schematic views in longitudinal section showing, respectively, handling of the carriers, lowering of the section of mobile rail to bring the lower carrier and the upper carrier, respectively, into the test position; Figures 14, 15, upper and 17 are schematic cross sections taken in the test area of the machine, showing a sequence of stages during testing of a printed circuit board positioned on the lower carrier; Figure 18 shows the supporting device of a lower adapter; Figure 19 is an enlarged illustration of the detail A in figure 8, Figures 20 and 21 show the detail of the supporting device of the lower adapter in the resting and testing state, respectively, Figure 22 is a schematic plan view of the support device for an upper adapter; Figure 23 is a view along the line XXIII-XXIII in Figure 22, also showing an adapter; Figure 24 is a view in the direction of the arrow XXIV in Figure 22. With particular reference to the numerical symbols in the above figures, a machine for carrying out the simultaneous electrical test on both sides of a printed circuit board is illustrated and described but clearly the same machine can be used to test just one side of the board. Such a machine comprises a frame, indicated as a whole by reference number 1, which supports a press 2 with parallel surfaces, which preferably has a stroke of 400 mm. The frame 1 has a loading area 3, a test area 4 and a parking area 5 of the press head 100. The loading area 3 is advantageously situated at one end of the machine, to facilitate the incoming flow of the boards to be tested and so as to be directly accessible to an operator, whether automatic or manual. The test area 4 may be situated in the center, to reduce transport time, but in this case it is poorly accessible if the apparatus is used without a carrier, with manual loading of the boards. The test area 4 is preferably positioned on the opposite side to the loading side, thus making the test area more accessible for manual operations. It is clear, however, that other arrangements are possible besides the one illustrated. With the arrangement shown in the appended figures, therefore, it is possible to pass without any modifications from use of the machine with a carrier to operation of the machine directly on the adapter, placed in the test area. The workstation can be varied extremely easily, in that the control terminal, indicated by 7 (Figure 3), can easily be moved from one workstation to the other. Alternatively, two mutually exclusive terminals 7 could be used, each positioned in a respective work station 3 or 4. In the case of operation of the machine with manual loading, as shown in figures 3 to 6, the operator positions the piece for testing directly on the adapter, in the test area 4, as will be better described below. This is facilitated by the fact that the head 100, besides moving vertically, on columns 101 (see also figures 7 and 8), by means of vertical screws (102), withdraws to the parking area 5 towards the center of the machine (Figure 3), sliding horizontally on longitudinal guide members 103, as will be better described below. Subsequently, when the operator presses a double push-button control, the test area is closed, with the return to the closed position of the upper head 100, and the press is closed (Figure 4). At the end, again on a double-push-button command by the operator, the press is opened (Figure 5) and the upper head moves to the parking area, thus allowing the operator to replace the piece and start a new cycle (Figure 6). The test data are provided by machine terminal 7. To effect opening of the upper head 100, that is the horizontal translation movement, opening means are provided which are shown more clearly in Figure 9 and in the diagram in Figure 10 and are indicated as a whole by reference number 10. Said opening means comprise a continuous current electric motor 11, with position control, which, by means of toothed belts 12, acts on a threaded rod system 13, that operates a mobile frame 14. The presence of a continuous current motor with position control allows the degree of opening value to be adjusted, in order to optimize the stroke and reduce testing time. For correct positioning of the upper head 100 in the test area 4, a system of rigid mechanical stops 105 is provided, disposed on longitudinal members 103 as shown in the diagram in Figure 10, against which the head 100 abuts. A spring cartridge 106 is interposed to avoid dangerous load conditions of the motor 11. Obviously other means are possible for opening of the upper head 100, which may, for example, take place with rotation about a fulcrum of the upper head or, preferably, with rotary translation of the upper head itself. Alternatively, a press stroke exceeding one meter could be foreseen, in order to allow good access to the electrical contact area, without having any horizontal head movement and, in practice, creating a parking area positioned above the test area 4. In the case of operation of the machine with automatic, or rather semi-automatic, loading, as shown in Figures 11-13c, a system of two carriers 120, 121 is used to carry the circuits for testing from the loading area 3 inside the press, or test area 4. Such carriers 120, 121 have a perforated support for passage of the test needles. The two carriers move on parallel planes one above the other. They always move in opposite stokes: when one carrier is in the test position the other is in the loading position. The system that allows movement of the carriers 120, 121 is made up of two rails 130, each carrying two staggered seats 122 and 123 one on top of the other in which endless elastic belts indicated as a whole by 125 run, moved by an electric motor 126 (Figure 1). On the rails 130 there is a series of pulleys 127 that allow the movement of the belts. The carriers receive traction from the belts by simple friction, not being in any way constrained to them for reasons of operator safety. Each rail 130 guides an endless belt on the seats 122, 123 from the loading area 3 to the test area 4, and is divided into two sections 131, 132: section 132 is in the test area 4 and follows the vertical movement of the head 100 to allow the carrier 120 or 121 to position the printed circuit 200 on the lower test apparatus, whilst the section 131 that is situated in the loading area remains at a constant height to allow the circuits to be loaded and unloaded from the carriers. The height of the entire carrier handling system, that is the system of rails 130 and elastic belts 125, can in turn be adjusted to allow the machine to adapt to test apparatus of different sizes, as will be better explained below. The rail section 132 that is situated in the test area 4 is constrained to the section 131 of the loading zone by means of an articulated parallelogram mechanical system (135) that ensures that the two rail sections 131, 132 are maintained parallel to each other even when the test area section 132 moves vertically to follow the head 100. The alignment of the two sections is ensured by special mechanical stops and by the force provided by a pre-loaded spring 136. From figures 13a-13c it can be noted that the use of elastic belts 125 makes it possible to follow the change in the center distance between the terminal pulleys resulting from the rotation of the parallelogram 135, without any need for systems to provide or take up tension. The correct working tension of the belt is obtained by adjusting the length of the belt itself: The correct position of the carrier 120 or 121 both in the loading area and in the test area, is determined by the respective mechanical stops 140, 141 (Figure 11). Each mechanical stop has a sensor to detect the presence of the carrier in the correct position. The machine checks that the sensors are both active before stopping the belt drive motor. In the fleeting interval of time necessary for the sensors to be activated simultaneously, the elastic belts slide on the carrier which is already positioned against the mechanical stops; this is possible because there is no constraint between the belts and the carriers. Connected to the upper head 100 there is a pressure device 150 which comes into contact with the structure of the mobile rail 132 to cause it to move: the height of said device 150 can in turn be adjusted by means of a screw system 151 (see also figures 14-17) to accommodate different sizes of upper test apparatus on the machine. With reference to Figures 14 to 17, the stages of testing a printed circuit indicated by reference number 200 will now be described briefly. In these figures the printed circuit 200 is positioned on the lower carrier 121, and the test is to take place simultaneously, both on the lower side and on the upper side, but clearly it would make no difference if the printed circuit 200 were placed on the upper carrier 120 or directly on the lower test apparatus, in the case of manual loading, in which the carriers 120 and 121 are removed from the machine. It is also obvious that the test can be carried out only on the lower side of the printed circuit 200, in which case the upper test apparatus is missing. In Figures 14 to 17 the means that allow the machine to operate with adapters of different types are illustrated and will be described below. These figures are schematic cross-sections taken in the test area 4 of the machine. Figure 14 corresponds to the position in which the carrier 121, which conveys the circuit 200, is halted through the effect of the mechanical stop 141 and the upper part of the press, indicated as a whole by the reference number 201, is about to start its descent, the lower part being indicated by reference number 202. Figure 15 shows the position in which, as a result of the vertical downward movement of the upper part 201 of the press, the pressure system 150 comes into contact with the mobile section 132 of the guide rails 130 of the elastic belts 125 that convey the carriers. Figure 16 shows the machine set-up at the moment when, as a result of the vertical movement of the press, the pressure system 150 lowers the mobile section 132 of the rails 130, bringing the carrier 121 into contact with the lower test adapter, allowing the cirucit to come into contact with the centering devices of the adapter itself Figure 17 shows the machine set-up in the position in which the vertical movement of the upper part 201 of the press stops and the electrical test is carried out on the circuit 200. In this position the pressure system 150 has lowered the mobile section 132 of the rails 130 to a lower height than that of the carrier 121, deposited together with the circuit 200 on the lower adapter 31, which will be recalled below. As is known, the test consists of checking that all the nets present on the printed circuit board 200 are insulated from each other and that there is electrical continuity between the points in each net. This is done by means of electrical contacts with well defined points in the circuit. For this purpose, a constant gauge grid, or needle bed, is used for each side of the circuit board to be tested, comprising a plurality of elastic electrical contacts, and a translation element or adapter, in which a number of needle contacts or pins corresponding to the number of points to be tested on the electrical circuit is arranged, said pins establishing an electrical connection between the corresponding needles in the grid and the points in the printed circuit 200. In the attached figures from 14 to 17, the lower grid or needle bed 22 is disposed in the lower head 300 of the press, and the lower adapter 31 cooperates with it, as will be described shortly. The upper grid or needle bed 220, on the other hand, is disposed in the upper head 100 of the press, and the upper adapter 50 cooperates with it. According to the invention, provision is made for the circuit testing press assembly to accommodate various types of adapters 31 or 50. With reference firstly to the lower part 202 of the press, on referring to figures 18 to 21 it will be noted that in order to allow the adapter 31 to be installed on the machine, it must be supported elastically so that the needles 30 do not compress the spring contacts 24 of the grid 22 and the grid itself can activate press stroke control sensors 160, which are normally at the four comers of the grid 22, only one of which is shown schematically in Figure 20; in addition, the right pressure must be exerted on the elastic means, in relation to the distance d (positive or negative) by which the adapter needles protrude towards the grid To achieve these aims, use is made of a sheet 20 of insulating material, preferably made of a fiberglass and epoxy resin laminate. The external dimensions of the sheet 20 must be sufficient to rest on supporting springs 21 provided on the edge of the contact grid 22; the sheet 20 has through holes 23 for the free passage of the spring contact elements 24 of the grid. The adapter 31 is set down on the sheet 20 and positioned by means of centering pins which engage in special holes provided both on the adapter and on the sheet. The test needles 30 that protrude from the lower side of the adapter 31 enter the holes 23 in the sheet 20 to come into contact with the grid 22 below. To avoid having to change the setting of the press stopping device when the type of adapter in use changes, the thickness S of the sheet on which the press stopping sensors 160 act must be chosen so as to be the same as the height h, during compression, of the spring contact 24 of the grid 22, plus the distance d by which the test needles 30 protrude from the lower side of the adapter, less the press stopping height q. Hence the relation S = h + d- q. The thickness S of the sheet 20, added to the height of the sheet from the grid base 22 when resting Q and less the amount d by which the test needles protrude, must be greater than the resting height H of the spring contact 24 of the grid (S + q - d > H) so that, when resting, the needles 30 do not rest on the spring contacts 24. This system allows the lower adapter 31, which is smaller at its perimeter than the sheet 20, to be placed in a generic position; during the test, the sheet 20 varies its distance from the test grid, compressing the supporting springs 21 on the grid perimeter, thanks to the pressure exerted by the adapter. If the resultant of the elastic reactions of the perimeter springs 21 of the grid does not coincide with the resultant of the pressures exerted by the adapter, the sheet 20 is disposed so that it is not parallel to the plane of the test grid. Under the action of the system of forces previously described, the sheet 20 can buckle; the possible buckling, in addition to the fact that the sheet and the grid are not parallel, could cause errors in control of the press movements. To limit these errors, distance pieces can be installed on the sheet 20, at the four corners. The thickness of these distance pieces 270, shown in Figures 20-23, must be such that the upper part 201 of the press, namely the part of the test system that exerts pressure on the sheet 20 and adapter 31 system, contacts the circuit 200 being tested and the distance pieces 270 simultaneously. Thus the edge of the sheet 20 and the adapter 31 are forced to move in an identical manner. This is achieved, as can be seen in Figure 23 in particular, by providing knurled screws 275 at the support system for the upper adapter 50, that come into contact with the tops of the distance pieces 270. The screws 275 are adjusted to compensate for the thickness of the printed circuit board 200 being tested. In the case of adapters 50 for testing the upper side of the circuit 200, besides what has already been seen for the lower adapter 31, as shown in Figures 20-23, the problem must also be overcome of supporting the adapter, whatever its dimensions, within the working area of the machine. The supporting device, which allows a generic adapter 50 to be suspended from the upper test grid 220, comprises a sheet 40, identical to the lower sheet 20, of insulating material equipped with through holes according to a grid identical to the test grid, to which two metal rods 41 are fixed, on the two opposite sides to the board itself. . The above mentioned rods serve as a guide for two slides 42, each of which supports a cross rod 43, to which are connected blocks 44 which can slide, but not rotate, with respect to the rod 43. The rod 43 can rotate around its own longitudinal axis and ends in an external crank 45 integral with one end of the rod 43 and equipped, in a median portion, with a slot 46, shaped like a portion of circumference, in which a locking handle 47 screws to fix the angular position of the rod 43. The operating principle is as follows: the adapter 50 is positioned in contact with the plate 40, while the two slides 42 are brought to the outermost open positions possible. The crank 45 is then operated, positioning the two slides so that the flanges, or edges, of the blocks 44 are inserted beneath the edge of the plate 50 of the adapter; if necessary, the position of the blocks along the rod 43 should be adjusted so that their flanges can be inserted beneath the edge of the adapter plate 50. By means of the crank 45, the rod 43 is rotated so that the flanges of the blocks 44 exert pressure on the plate 50, towards the plate 40. Once the positioning is completed, the threaded locking handle is tightened, so that the crank 45 is locked by friction against the sliding shoe 500 of the slide 42. In this manner, the crank 45 being rigidly connected to the rod 43 since the blocks 44 cannot rotate with respect to the rod, the adapter is supported and rigidly constrained to the plate 40. The plate 40 is of a thickness calculated so that at the end of the press movement the test needles 30' exert the correct compression on the spring contacts of the upper grid. Since the adapters are reciprocally positioned, through the use of reference pins, one of the two must be allowed a certain freedom of movement. Therefore, the plate 40 can be constrained to the upper grid 220, with supports that hold it at a suitable distance from the test grid, and is positioned with respect to it by means of reference pins that engage in holes with a certain play, preferably 0.3 mm. In this manner, when, because of the movement of the press, the upper adapter/support device assembly comes to rest on the lower adapter, closing the circuit 200 (fig. 17), before the upper test grid enters into contact with the plate 40, reciprocal centering of the adapters can take place. To favour this possibility of reciprocal centering of the adapters, it is possible to roughly position the upper adapter with respect to the plate 40, by means of two pins installed on the plate 40 which engage in the holes provided for this purpose on the adapter plate. The diameter of the two holes is about 0.3 mm larger than that of the two pins, so that the adapter is free to move with respect to the plate 40. In order to exploit this freedom of movement, the support system has to be positioned with the flanges of the blocks 44 under the edge of the adapter plate, without turning the crank 45 upwards, in order to block the plate 50 against the plate 40. The size of the crank 45 is such that if the threaded handle 47 is not tightened, the flanges of the blocks 44 remain horizontal, preventing the adapter from falling. The slides 42 are locked in this position by means of a screw 520, provided on the slides 42, which tightens against the rods 41. From what is described above, it can be seen that the invention achieves the proposed aims. An important aspect lies in the fact that it is possible to use adapters of various makes, with simple and rapid adaptation to the apparatus. The invention, thus conceived, lends itself to numerous variants and modifications, all coming within the scope of the concept of the invention. Moreover, the materials employed, provided they are compatible with the specific use, and the dimensions and contingent shapes can be of any kind, according to requirements. Although the press assembly according to the invention has been described with reference to a particular test machine, it is evident that such press assembly can be used with any type of test machine.

Claims: A press assembly for performing the electrical test on at least one side of a printed circuit board (200), comprising an upper part (201) and a lower part (202), between which the circuit (200) to be tested is placed, resting on a lower adapter (31), bearing a plurality of needles (30) that can be brought into contact with corresponding spring contacts (24) of a constant gauge grid or needle bed (22), characterized by the fact that an interchangeable insulating sheet (20) is disposed between said adapter (31) and said grid (22), wherein the insulating sheet is selected from sheets of variable thicknesses in accordance with the type of adapter (31) used, the sheet (20) being provided with holes (23) for the passage of the adapter needles (30). A press assembly according to claim 1, characterized by the fact that said sheet (20) rests on springs (21 ) on the grid (22) and its thickness (S) is equal to the height during compression (h) of the spring contacts (24) of the grid (22) plus the distance (d) by which the needles (30) protrude from the adapter towards the grid, less the press stopping height (q). A press assembly according to claim 1 or 2, characterized by the fact that the thickness (s) of said sheet (20), added to the resting height Q of the sheet with respect to the grid (22) and less the distance (d) the test needles protrude from the adapter (31), is greater than the resting height (H) of the spring contacts (24) of the grid. A press assembly according to any one of claims 1 to 3, in which said upper part (201) of the press assembly also comprises an upper adapter (50) and relative constant gauge grid (220), characterized by the fact that a second sheet of insulating material (40) is foreseen, serving the same purpose as the lower sheet (20), constrained to said grid (220) and also provided with means for supporting the adapter (50). A press assembly according to claim 4, characterized by the fact that said supporting means comprise two longitudinal rods (41) acting as guide elements in which two slides (42) run, each supporting a cross rod (43) to which are connected sliding blocks (44) that are rotably integral with the rod (43) which can rotate around its own longitudinal axis and ends in a crank (45) equipped, in a middle portion, with a slot (46) shaped like a portion of circumference, inside which a locking handle (47) operates, so that the blocks (44) can be brought into locking engagement with the adapter (50). A press assembly according to any one of claims 1 to 5, characterized by the fact that distance pieces (270) are provided that act, through adjusting means (275), between said lower sheet (20) and said upper sheet (40), to impose the same movements on the lower sheet (20) and on the lower adapter (31) during the press stroke to perform the test on the circuit (200). A press assembly according to anyone of the previous claims characterized in that said circuit board to be tested is supported on a carrier (120, 121). A press assembly according to anyone of the previous claims supported on a frame (1) of a machine for electrically testing at least one side of a printed circuit board (200), characterized in that said frame (1) has a loading area (3), a test area (4) and a parking area (5) for the press head (100), means for moving said head (100) from the test area (4) to the parking area and vice versa, to allow manual loading of the circuit boards (200) in the test area and means for automatically transferring the circuits from the loading area (3) to the test area (4) and vice versa, thus creating two distinct work stations, one at said loading area (3) and the other at said test are (4), that can be used selectively by a single operator.

Inventors: NUCCI FERNANDO, NUCCI, FERNANDO
Applicants: MANIA TECNOLOGIE ITALIA S P A, MANIA TECNOLOGIE ITALIA S.P.A.
Application year: 1994
Main classification: G01R1
IPC codes: G01R31, G01R1